1. Field of the Invention
The present invention relates to a tube lens used for a microscope, an imaging optical system and a microscope that has the tube lens.
2. Description of the Related Art
A tube lens of a microscope is a lens for collecting parallel light flux from an objective, and enlarges and projects the light from an object on the sample surface onto the image surface. Accordingly, with the microscope, an object may be observed as an enlarged image, while the aberration on the image surface needs to be corrected in order to obtain an enlarged image of a good quality.
As a scheme to correct aberration on the image surface, the compensation free scheme in which the objective and the tube lens individually correct aberration to correct aberration on the image surface has been known, and has been widely used conventionally. Various tube lenses that are suitable for the compensation free scheme have been proposed and disclosed in Japanese Laid-open Patent Publication No. 2004-144932, Japanese Laid-open Patent Publication No. 2003-75720, Japanese Laid-open Patent Publication No. H4-93911, for example.
In the compensation free scheme, the object may be observed with an enlarged image of a good quality by using an objective and a tube lens for which aberration is corrected in a good condition respectively.
Incidentally, in recent years, as one of applications of a microscope, the virtual slide system has attracted attention. The virtual slide system is a system in which a pathological sample is scanned to capture its images at a certain level of high magnification, and a large image that displays the entirety of the pathological sample (hereinafter, referred to as a virtual slide image) is generated by joining the obtained images of different areas of the pathological sample (hereinafter, referred to as original images), and the generated virtual slide image is used for pathological diagnosis. Since the virtual slide system enables pathological diagnosis at a distant place through a network, it is expected as an effective solution for problems such as increases in the number of diagnosis and uneven distribution of pathologists.
Since the virtual slide image is displayed while being enlarged or contracted as needed, it needs to have a sufficient resolution that is good for enlarged display. Therefore, the image of the pathological sample needs to be captured at a certain level of high magnification.
However, the greater the magnification for imaging, the smaller the areas of the pathological sample captured in a original image, leading to an increase in the number of original images required for generating the virtual slide image. In addition, since the virtual slide image is generated by joining the original images, there is a need to suppress change in the image quality between the center part and the peripheral part of the original image.
For this reason, in order to realize a virtual slide system of a high throughput that generates a virtual slide image of a good image quality, the tube lens used for the virtual slide system needs to have a wide field of view, and the curvature of the image surface needs to be corrected in a good condition within the range of the field of view.